This chapter explores the legal implications of autonomous weapon systems and the potential challenges such systems might present to the laws governing weaponry and the conduct of hostilities. Autonomous weapon systems are weapons that are capable of selecting and engaging a target without further human operator involvement. Although such systems have not yet been fully developed, technological advances, particularly in artificial intelligence, make the appearance of such systems a distinct possibility in the years to come. In fact, several experts predict autonomous weapons will become the norm on the battlefield within twenty years. Given such a possibility, it is essential to look closely at both the relevant technology involved in these cutting-edge systems and the applicable law. This chapter commences with an examination of the emerging technology supporting these sophisticated systems, by detailing autonomous features that are currently being designed for weapons and anticipating how technological advances might be incorporated into future weapon systems. A second aim of the chapter is to describe the relevant law of armed conflict principles applicable to new weapon systems, with a particular focus on the unique legal challenges posed by autonomous weapons. The legal analysis will outline both how autonomous weapon systems would need to be designed for them to be deemed lawful per se, and whether the use of autonomous weapons during hostilities might be prohibited in some manner under the law of armed conflict. The third and final focus of this chapter is to address potential lacunae in the law dealing with autonomous weapon systems. In particular, the author will reveal how interpretations of and issues related to subjectivity in targeting decisions and overall accountability may need to be viewed differently in response to autonomy.